U.S. Pat. No. 3,630,879 issued Dec. 28, 1971, in the name of Spacil et al., describes a solid oxygen ion electrolyte cell structure having a cylindrical form free of electrical conductors said to be useful to generate hydrogen gas by dissociation of water. Patentees describe the structure as a thin continuous cylinder of "internally short-circuited" solid oxygen ion material having a first continuous porous electrode over its inner surface and a second continuous porous electrode over its outer surface.
Ounalli et al. in "Hydrogen Production By Direct Thermolysis Of Water On Semipermeable Membrane", C. R. Acad. Sci. Paris. t. 292 pp. 1185-1190 (1981), report use of a single phase mixed conductor as an oxygen semipermeable membrane. A membrane of calcia stabilized zirconia at temperatures in a range of 1400.degree. C. to 1800.degree. C. is stated to extract oxygen from steam to produce hydrogen, and that oxygen was transported through the membrane.
U.S. Pat. No. 4,330,633 issued May 18, 1982, in the name of Yoshisato et al., describes a solid electrolyte said to selectively separate oxygen from a gaseous atmosphere having a high oxygen partial pressure into a gaseous atmosphere having a low oxygen partial pressure. Patentees describe the solid electrolytes as composed of a sintered body consisting essentially of an oxide of cobalt, an oxide of at least one metal selected from strontium and lanthanum, and an oxide of at least one metal selected from bismuth and cerium.
U.S. Pat. No. 4,659,448 issued Apr. 21, 1987, in the name of Gordon, describes a process for removal of SO.sub.x and NO.sub.x from flue gases using a solid state electrochemical ceramic cell. Patentee states that the process requires application of an external electrical potential to electro-catalytically reduce SO.sub.x and NO.sub.x to elemental sulfur and free nitrogen gas. Oxygen apparently is removed through the solid electrolyte in what amounts to electrolysis.
U.S. Pat. No. 4,791,079 issued Dec. 13, 1988, in the name of Hazbun, describes a mixed ion and electron conducting catalytic ceramic membrane said to be useful in hydrocarbon oxidation or dehydrogenation processes. Patentee describes the membrane as consisting of two layers, one of which is an impervious mixed ion and electron conducting ceramic layer and the other is a porous catalyst-containing ion conducting ceramic layer. This impervious mixed ion and electron conducting ceramic membrane is further described at column 2, lines 57-62, as yttria stabilized zirconia which is doped with sufficient cerium oxide, CeO.sub.2, or titanium oxide, TiO.sub.2, to impart electron conducting characteristics to the ceramic.
Numerous publications describe conventional fuel cells which completely oxidize methane to carbon dioxide and water. Fuel cells are not designed to control partial oxidation processes which produce added-value products, but rather to generate electricity from fuel gas and air (or oxygen). Processes conducted in fuel cells are selected for complete oxidation of fuel to relatively valueless combustion products and require completion of an external electric circuit for oxidation of fuel gas to proceed. See, for example, U.S. Pat. No. 4,476,196 issued Oct. 9, 1984, in the name of Poeppel et al., U.S. Pat. No. 4,476,198 issued Oct. 9, 1984, in the name of Ackerman et al., or U.S. Pat. No. 4,883,497 issued Nov. 28, 1989, in the name of Claar et al.
U.S. Pat. No. 4,877,5063 issued Oct. 31, 1989, in the name of Fee et al., describes an electrically operated, solid electrolyte oxygen pump having a one-piece, monolithic ceramic structure said to afford high oxygen production per unit weight and volume and thus particularly adapted for use as a portable oxygen supply. Patentees describe the one-piece structure as comprised of thin ceramic layers of cell components including air electrodes, oxygen electrodes, electrolyte layers, and interconnection materials. The oxygen pump is not designed to conduct chemical processes, but rather to remove oxygen from air to form a higher concentration of oxygen. The processes transferring oxygen across a solid electrolyte barrier in the oxygen pump require an external electric circuit including a source of electrical potential, DC voltage across the electrodes, for transfer to proceed.
European Patent Application 90305684.4, published on Nov. 28, 1990, under Publication No. EP 0 399 833 A1 in the name of Cable et al., describes an electrochemical reactor using solid membranes comprising; (1) a multi-phase mixture of an electronically-conductive material, (2) an oxygen ion-conductive material, and/or (3) a mixed metal oxide of a perovskite structure. Reactors are described in which oxygen from oxygen-containing gas is transported through a membrane disk to any gas that consumes oxygen. Flow of gases on each side of the membrane disk in the reactor shell shown are symmetrical flows across the disk, substantially radial outward from the center of the disk toward the wall of a cylindrical reactor shell. The gases on each side of the disk flow parallel to, and co-current with, each other.
Materials known as "perovskites" are a class of materials which have an X-ray identifiable crystalline structure based upon the structure of the mineral perovskite, CaTiO.sub.3. In its idealized form, the perovskite structure has a cubic lattice in which a unit cell contains metal ions at the corners of the cell, another metal ion in its center and oxygen ions at the midpoints of each cube edge. This cubic lattice is identified as an ABO.sub.3 -type structure where A and B represent metal ions. In the idealized form of perovskite structures, generally, it is required that the sum of the valences of A ions and B ions equal 6, as in the model perovskite mineral, CaTiO.sub.3.
Many materials having the perovskite-type structure (ABO.sub.3 -type) have been described in recent publications including a wide variety of multiple cation substitutions on both the A and B sites said to be stable in the perovskite structure. Likewise, a variety of more complex perovskite compounds containing a mixture of A metal ions and B metal ions (in addition to oxygen) are reported. Publications relating to perovskites include: P. D. Battle et al., J. Solid State Chem., 76, 334 (1988); Y. Takeda et al., Z. Anorg. Allg. Chem., 550/541,259 (1986); Y. Teraoka et al., Chem. Lett., 19, 1743 (1985); M. Harder and H. H. Muller-Buschbaum, Z. Anorg. Allg. Chem., 464, 169 (1980); C. Greaves et al., Acta Cryst., B31, 641 (1975).
However, a recurring problem that is common to many such compositions and membranes is that they often tend to break, fracture, and/or a undergo phase change and thereby to lose their ability to selectively separate and/or transport the desired gaseous material, after relatively short period of time under commercial conditions of operation, i.e., pressure drop across the membrane, elevated temperatures of operation, changes of temperature, temperature differentials, and the like.